Two substitutions at an identical location in the ligand-binding domain (LBD) of the human androgen receptor (AR), R855C and R855H, are associated with complete androgen insensitivity syndrome (CAIS) and partial AIS (PAIS), respectively. Kinetic analysis of the mutant receptors in genital skin fibroblasts (GSF) and in transfected cells revealed very low total binding (B_max) and increased rate constants of dissociation (k) for the R855C mutant; and normal B_max and k, with slightly elevated equilibrium affinity constants (K_d), but decreased transactivational capacity for the R855H mutant. Further analysis of the R855H mutant revealed both thermolability and decreased N/C terminal interactions in the presence and absence of the coactivator TIF-2. To establish the nature of these functional differences we have used molecular dynamic (MD) modeling to create 4D models of each of the mutant receptors. Molecular dynamic modeling produced profoundly different models for each of the mutants: in modeling of R855C a surprisingly significant distant alteration of helix 12 positioning of the AR ligand binding domain (AR-LBD) occurs, which would predict severe ligand binding abnormalities and CAIS; in modeling of R855H no dramatic effect on the position of helix 12 was seen, thus binding properties of the receptor are not compromised.

Molecular dynamics 4D modeling clearly supports the biochemical and kinetic studies of both mutants. Such novel computational modeling may lead to a better understanding of the structure function relationships and the molecular mechanics of ligand binding not only of the AR-LBD but also for other nuclear receptors.